There has been a rapid expansion in the area of terahertz technology, apparatus and components using THz technology. The feasibility of various THz applications has been greatly expanded due to the development of spectroscopy and imaging methods such as THz time-domain spectroscopy (THz TDS) and continuous wave (CW) THz imaging. One of the limitations in applying THz TDS to imaging has been the requirement for a scanning method that records the entire THz time-domain waveform. Most time-domain THz systems use slow mechanical scanning delay lines, or mirror shakers (15-300 Hz repetition rate)(Chan et al., “Imaging with terahertz radiation”, Rep. Prog. Phys. 70, 1325-1379 (2007)) to detect the THz waveform on a point by point basis. Improvements to the mechanical scanning method have included piezo-electric delay lines, which are reasonably fast (kHz) but are limited to a 10 ps scanning range, as well as a rotating scanning stage. J. Xu and X.-C. Zhang, “Circular involute stage”, Opt. Lett. 29 2082 (2004).
For the CW photomixing configuration, two laser sources are typically multiplied or mixed in a device such as a photoconductive antenna structure. THz radiation is generated at the difference frequency of the two laser sources. Some groups have used Golay cells, bolometers (J.-Y. Lu et al., “Optoelectronic-based high-efficiency quasi-CW terahertz imaging”, IEEE Photon. Tech. Letters 17, 2406 (2005)), or other power detection devices. Since the THz power, not electric field, is detected in these devices, the THz phase information is lost. However, no scanning of the THz waveform is required. For the coherent detection approach, the THz waveform is scanned by varying the phase (or arrival) of the THz waveform relative to the phase of the mixed laser beams. Following the example of THz TDS, a mechanically scanning delay rail (A. Nahata et al., “Free-space electro-optic detection of continuous-wave terahertz radiation”, Appl. Phys. Lett. 75, 2524 (1999); K. J. Siebert et al., “Continuous-wave all-optoelectronic terahertz imaging”, Appl. Phys. Lett. 80, 3003 (2002); N. Karpowicz et al., “Comparison between pulsed terahertz time-domain imaging and continuous wave terahertz imaging”, Semicond. Sci. Technol. 20, 293 (2005)) typically is used to vary the optical path of the two infrared laser beams after the beams have been combined. These delay rails are typically slow, not because a long waveform is recorded as is the case of the THz TDS systems, but rather because the delay induced by the scanning rail must be comparable in distance to the wavelength of the THz radiation (˜300 μm for 1THz).
Consequently there is the need for faster THz methods and devices and systems employing same.